The present invention relates to an optical element, a mold of producing the optical element, and a method of producing the optical element.
As the conventional methods for producing a conventional optical element, there is known, for example, a method for producing an optical element wherein molten glass or another optical material is filled into a mold having a cavity formed to the desired lens shape to produce a molded lens.
Also, there is known a method for producing an optical element wherein reactive ion etching (RIE) or another etching method is applied to etch an optical material to a desired lens shape by using a photoresist as an etching mask.
Further, there is known a method for producing an optical element wherein an optical material is mechanically polished to form a desired lens shape.
In a data storage apparatus such as a magneto-optic disk apparatus or DVD (digital versatile disk) apparatus an optical head is arranged close to the surface of a disk-like data recording medium and a converged laser beam is exposed onto a data recording media surface to record data on data recording medium or read data from the data recording medium.
When trying to raise a recording density of data in order to achieve a larger capacity of data recording in such a data storage apparatus, the laser beam must be sharply converged and exposed on the surface of the data recording medium, and it is necessary to use an object lens having a high numerical aperture (NA). In this case, if a large sized lens is used, the optical head ends up becoming large, then, a diameter of the lens must be kept at a small size. Accordingly, this means usage of a lens having a high numerical aperture and having a small size. As a result, it becomes necessary to arrange the lens extremely close to the surface of the data recording medium.
A floating type optical head operates in a state forming a thin air gap with the surface of the high speed rotating data recording medium and slightly floating from the surface of the data recording medium, so enables the lens to be arranged close to the surface of the data recording medium and, accordingly, is advantageous for achieving a higher density of recorded information. The floating type optical head can be constituted by the above optical element.
FIGS. 19A to 19E are views of production processes for producing an optical element applied to a conventional floating type optical head and show side sectional views of the optical element at different stages of the production process. Referring to these drawings, a method for producing a conventional optical element will first be explained. In this example, an object lens having a high numerical aperture obtained by combining an ordinary lens 2112 and a ball lens 2106 is used to form an optical element.
As shown in FIG. 19A, at the center of a flat slider substrate 2102 rectangular when seen from a plan view, first, a lens holding hole 2104 conical in shape and passing through the slider substrate 2102 is formed. As shown in FIG. 19B, a spherical ball lens 2106 is dropped into this hole 2104 and fixed by bonding, then a portion 2106A of the ball lens 2106 projecting from the lens holding hole 2104 is polished to the same level as the bottom surface of the slider substrate 2102 as shown in FIG. 19C. The bottom surface of the slider substrate 2102 flattened in this way and the bottom surface of the ball lens 2106 become surfaces slightly floating from the surface of the data recording medium.
Next, as shown in FIG. 19D, in order to form two floating use rails 2108 and 2108 at the two end portions of the bottom surface of the slider substrate 2102, two grooves 2110 and 2110 sandwiching the ball lens 2106 is formed by for example dry etching such as ion milling or RIE (reactive ion etching) and selective etching utilizing semiconductor photolithography.
Finally, a lens 2112 (for example, a molded glass lens) formed by another process is arranged and fixed by bonding on the slider substrate 2102 so as to close the opening of the lens holding hole 2104, whereby an optical element 2114 is completed.
In the above conventional method for producing an optical element, for example, the method for producing a molded lens, the formation of the cavity is troublesome in work.
In the above conventional method for producing an optical element, for example, the method for producing an optical element using RIE or another etching technique, the use of the optical material is restricted. There are few optical materials having a high refractive index giving a lens having a large numerical aperture NA among optical materials capable of RIE or other etching.
Also, a method of production for producing a plurality of optical systems is demanded from the viewpoint of reducing the production costs of optical systems.
Further, when forming a floating type optical head by using the above optical element, in order to record data on the data recording medium at a high density and reproduce data recorded at a high density from the data recording medium, it is necessary to sharply converge the laser beam and expose the converged beam on a specific position on the data recording medium with a good precision. Accordingly, when forming the conventional floating type optical head 2114, an extremely high precision is required particularly in the work for formation and assembly of the lens, the work took a long time, skill was necessary. Also, it was necessary to form the parts used with a very high precision too.
For example, the lens holding hole 2104 must be formed in the slider substrate 2102 with a high precision, and the ball lens 2106 must be arranged and fixed in the lens holding hole 2104 with a high precision. Also, in order to form the ball lens 2106 an extremely high sphericity and precision of radius are required. Further, in the polishing of the ball lens 2106 projecting from the lens holding hole 2104, it is necessary to control the amount of polishing with a high precision so that the polished level becomes the same as the surface of the slider substrate 2102. Further, when arranging the lens 2112 on the lens holding hole 2104 as well, the lens must be positioned with an extremely high precision of the xcexcm order three-dimensionally. This positioning has been conventionally carried out by observing aberration etc, and the lens 2112 has a shape as a double convex lens so is hard to handle. As a result, the work takes a long time and skill becomes necessary.
As discussed above, high precision parts are necessary and the work efficiency is poor, therefore, in the end, the cost becomes high. Further, since the lens 2112 is arranged on the lens holding hole 2104 and the lens 2112 projects from the slider plate 2102, such the condition is disadvantageous from the point of reduction of the size.
Accordingly, an optical element which can be easily produced and which is advantageous in realizing a floating type optical head with an inexpensive production cost, a production use mold useable for the production of the optical element, and a method for producing the optical element have been sought.
The present invention was made in order to overcome the above disadvantages.
Accordingly, an object of the present invention is to provide an optical element which can be easily produced and is inexpensive in production cost, a production use mold useable for the production of the optical element, and a method for producing the optical element.
According to the present invention, the following optical element is provided: This optical element is an optical element having a substrate made of an optical material, the optical element characterized in that one surface of the substrate is formed with a convex portion having a first curvature, another surface facing the convex portion of the one surface of the substrate is formed with a concave portion having a second curvature, and the concave portion is filled with an optical material having a refractive index different from the substrate.
The convex portion and the concave portion can have shapes axially symmetric or approximately axially symmetric with respect to their optical axes, a first flat portion can be formed around the convex portion in the one surface, a second flat portion can be formed around the concave portion in the other surface, and the first and second flat portions can be made parallel or approximately parallel to each other.
The surface of the optical material filled in the concave portion and the second flat portion can be made parallel or approximately parallel to each other.
The surface of the optical material filled in the concave portion and the second flat portion can be positioned on the identical plane or approximately identical plane.
The optical axes of the convex portion and concave portion can be positioned on an identical straight line or approximately identical straight line.
The radii of curvature of the surfaces of the convex portion and the concave portion can be made constant or approximately constant.
Alternatively, an optical element of the present invention is an optical element having a substrate made of an optical material, characterized in that one surface of the substrate is formed with a hole and a bottom of the hole is formed with a convex portion having a first curvature.
The other surface facing the one surface of the substrate can be formed with a concave portion having a second curvature.
The convex portion and the concave portion can have a shape axially symmetric or approximately axially symmetric around their optical axes, a first flat portion can be formed around the hole in the one surface, a second flat portion can be formed around the concave portion in the other surface, and the first and second flat portions can be made parallel or approximately parallel to each other.
The convex portion at the bottom of the hole can be positioned between a plane passing through the first flat portion and the second surface.
The optical axes of the convex portion and concave portion can be positioned on an identical straight line or approximately identical straight line.
The radii of curvature of the surfaces of the convex portion and the concave portion can be made constant or approximately constant.
The concave portion can be filled with an optical material having a refractive index different from the substrate.
The surface of the optical material filled in the concave portion and the second flat portion can be made parallel or approximately parallel to each other.
The surface of the optical material filled in the concave portion and the second flat portion can be positioned on an identical plane or approximately identical plane.
Alternatively, the optical element of the present invention is an optical element including a substrate made of an optical material and a lens supported on the substrate, characterized in that the substrate is formed by a transparent material of a first refractive index, the lens is formed as a lens obtained by filling a concave portion formed in one surface of the substrate with a transparent material having a second refractive index different from the transparent material, and a surface of the substrate on the lens side is formed with floating use rails integral with the substrate.
The substrate can be formed by silica-based glass.
The surface of the substrate on the lens side may be coated with a protective film made of a transparent material having a higher hardness than the transparent material forming the substrate and containing carbon as a principal component.
The surface of the substrate at the lens side and the protective film may have formed between them a second protective film made of a transparent material having a higher hardness than the substrate but having a lower hardness than the protective film.
The second protective film can be formed by alumina, silica-based material, or silicon nitride.
Alternatively, an optical element of the present invention is an optical element including a substrate made of an optical material and a lens supported on the substrate, the optical element characterized in that the substrate includes first and second substrates formed by transparent materials, the lens is formed as a lens obtained by filling a concave portion having a first curvature formed in one surface of the first substrate with a transparent material having a second refractive index different from the refractive index of the transparent material forming the first substrate, the second substrate is made of a transparent material having a higher hardness than the transparent material for forming the first substrate, the surface is arranged so as to face the surface of the first substrate on the lens side and be in close contact with the first substrate, floating use rails are formed on the surface of the second substrate on an opposite side to the first substrate integrally with the second substrate, and the surface of the second substrate on the floating rail side is coated with a transparent protective film having a higher hardness than the transparent material forming the second substrate and containing carbon as a principal component.
The transparent material forming the first substrate can be made silica-based glass.
The transparent material forming the second substrate can be made alumina, silica-based glass, or silicon nitride.
The protective film can be made a diamond-like carbon film.
A thickness of the protective film is preferably set to at least 5 nm.
Further, a production use mold of an optical element of the present invention is a production use mold of an optical element made of an optical material, characterized by comprising a cavity to be filled with the optical material in a molten state or a softened state and a first pin forming a convex portion or a concave portion with respect to the optical material in the cavity, wherein the first pin penetrates through a wall of the cavity from the outside, a front end of the first pin has a concave shape sunken with a first curvature at its center.
The front end of the first pin can have a shape axially symmetric or approximately axially symmetric with respect to the axial center.
At the front end of the first pin, a radius of curvature of the center portion can be made constant or approximately constant.
The first pin can be made one penetrating through the wall of the cavity from the outside and projecting into the cavity.
At the wall of the cavity, a periphery of a region through which the first pin penetrates can be made flat and the bottom of the concave shape in the front end of the first pin can be positioned between a plane passing through the periphery of the first pin at the wall of the cavity and an opposing wall facing the wall of the cavity.
The mold can further have a second pin for forming a positioning use mark at the optical material in the cavity, and the second pin can penetrate through the wall of the cavity from the outside.
Further, a method for producing an optical element of the present invention is a method for producing an optical element using a disk-like first substrate formed with a plurality of first lenses and a plurality of positioning use first marks and made of an optical material and a disk-like second substrate formed with a plurality of second lenses corresponding to the plurality of first lenses and a plurality of positioning use second marks corresponding to the plurality of positioning use first marks and made of an optical material to produce an optical element, the method for producing an optical element characterized in that an arrangement of center positions of the plurality of first lenses and the positions of the plurality of first marks on the surface of the disk-like first substrate coincides with the arrangement of center positions of the corresponding plurality of second lenses and the positions of the plurality of second marks on the surface of the disk-like second substrate and in that the method includes a step of bonding the first and second substrates so that the first and second marks are superimposed and a step of separating the bonded first and second substrates into individual optical elements comprised by the first and second lenses.
The plurality of first marks can be formed on an opposing surface facing the second substrate in the surface of the first substrate, and the plurality of second marks can be formed on an opposing surface facing the first substrate in the surface of the second substrate.
The first substrate can be formed with a plurality of holes corresponding to the plurality of first lenses, bottom surfaces of the plurality of holes can be formed with convex portions having axially symmetric shapes about their axial centers, and the convex portions can constitute the first lenses.
Alternatively, a method for producing an optical element of the present invention is a method for producing an optical element including a substrate made of an optical material and a lens supported on the substrate, the method for producing an optical element characterized by including the steps: preparing a transparent substrate having a lens formed by filling a concave portion of one surface with a transparent material, forming a photoresist film on the surface of the substrate at the lens side, patterning the lens portion and the photoresist film to the shape of a support by photolithography, dry etching the surface of the substrate using the photoresist film as a mask to form grooves, then removing the photoresist film to obtain the optical element.
The substrate can be formed by glass.
After removing the photoresist film, the surface of the lens side of the substrate can be coated by a protective film having a higher hardness than the transparent material forming the substrate and containing carbon as a principal component.
After removing the photoresist film and before the formation of the protective film, the surface of the substrate can be formed with a second protective film made of a transparent material having a higher hardness than the substrate but having a lower hardness than the protective film.
The second protective film can be formed by alumina, silica-based glass, or silicon nitride.
Alternatively, a method for producing an optical element of the present invention is a method for producing an optical element including a substrate made of an optical material and a lens supported on the substrate, the method for producing an optical element characterized by including the steps of: preparing a transparent first substrate having a lens formed by filling a concave portion of one surface with a transparent material, depositing on the surface on the lens side of the first substrate a transparent material having a higher hardness than the first substrate to obtain a second substrate in close contact with the first substrate, forming a photoresist film on the surface of the second substrate at the side opposite to the first substrate, patterning the photoresist film to the shape of floating use rails by photolithography, dry etching the surface of the second substrate using the photoresist mask as a mask to form grooves in the surface of the second substrate, then removing the photoresist film to obtain the optical element.
Alternatively, a method for producing an optical element of the present invention is a method for producing an optical element including a substrate made of an optical material and a lens supported on the substrate, the method for producing an optical element characterized in that the optical element is formed by bonding with a transparent first substrate having a lens formed by filling a concave portion of one surface with a transparent material a second substrate made of a transparent material having a higher hardness than the first substrate while making its surface face the surface on the lens side of the first substrate and in that it comprises the steps of: forming a photoresist film on the surface of the second substrate on the opposite side to the first substrate before bonding the second substrate to the first substrate or after bonding the second substrate to the first substrate, patterning the photoresist film to the shape of floating use rails by photolithography, dry etching the surface of the second substrate using the photoresist mask as a mask to form grooves in the surface of the second substrate, then removing the photoresist film to obtain the optical element.
The first substrate can be formed by glass.
The second substrate can be formed by alumina, silica-based glass, or silicon nitride.
After removing the photoresist film on the second substrate, a protective film having a higher hardness than the second substrate and containing carbon as a principal component can be formed on the surface of the groove side.
The protective film containing carbon as a principal component can be a diamond-like carbon film.
The protective film is preferably formed to a thickness of at least 5 nm.